This invention pertains to drill pipe used in rotary drilling of the earth and more particularly to such drill pipe incorporating a sleeve thereabout to protect the pipe against wear.
A description of the prior art of drill pipe protectors appears in the aforementioned U.S. Pat. No. 4,146,060.
The process of centrifugally casting metals such as steel and of such casting incorporating two different materials, i.e. dual metal centrifugal casting is known and is described for example in a publication constituting the general catalog of the Industrial Products Division of United States Pipe and Foundry Company, bearing the notation "10-75" on the back thereof.
The aforementioned catalog describes various applications of dual casting, for example, on pages 23-24 is described a roll shell having an exterior of "Alloy 250", which is a hard alloy steel, and an interior of ductile iron, the shell being shrink fitted to a mandrel to produce a roll. Other applications are described.
A search relative to differential casting for the purpose of incorporating solid hard particles, e.g. tungsten carbide, in the outer surface of a tool joint or drill pipe protector resulted in the following references to U.S. patents:
______________________________________ 1,954,892 Russell et al 3,103,722 Whitehurst 2,129,382 Diwowarsky 3,175,260 Bridewell et al 2,207,150 Hirsch et al 3,468,997 Pickels 2,262,983 Woods ______________________________________
A search relative to smooth hard faced tool joints resulted in the following references to U.S. patents:
______________________________________ 3,989,554 3,380,861 1,496,979 3,819,364 3,092,491 3,067,593 3,215,510 2,833,638 3,260,579 3,790,353 ______________________________________
See also brochure of Reed Tool Company: "We're Wearing Out Casing So You Won't.
Other patents relating to hard facing include:
______________________________________ 1,924,099 Bain et al 3,175,427 Bridwell et al 2,033,638 Owen 3,258,817 Smiley 3,127,945 Bridwell et al 3,293,012 Smiley 3,128,165 Bridwell et al 3,301,645 Smiley 3,149,411 Smiley et al 3,301,673 Smiley 3,175,260 Bridwell et al ______________________________________